Gaokao Exam Biology: Genetics and Evolution

Question 1

In a monohybrid cross between two heterozygous parents (Aa × Aa), what is the expected phenotypic ratio in the offspring?

Accepted Answer

3:1

Answer

A Punnett square for Aa × Aa yields AA, Aa, Aa, aa — a 3:1 dominant-to-recessive phenotypic ratio.

Question 2

Which molecule carries the genetic instructions from the nucleus to the ribosome during protein synthesis?

Accepted Answer

mRNA

Answer

Messenger RNA (mRNA) transcribes the DNA code in the nucleus and carries it to ribosomes for translation.

Question 3

Darwin's theory of natural selection is best described as:

Accepted Answer

Individuals with favorable traits survive and reproduce more successfully

Answer

Natural selection states that heritable traits increasing survival and reproduction become more common over generations.

Question 4

A sex-linked recessive trait is carried on the X chromosome. If the mother is a carrier (X^A X^a) and the father is unaffected (X^A Y), what percentage of their sons will be affected?

Accepted Answer

50%

Answer

Sons receive either X^A (unaffected) or X^a (affected) from the mother with equal probability, so 50% of sons are affected.

Question 5

Which term describes a mutation that changes a single nucleotide base in the DNA sequence?

Accepted Answer

Point mutation

Answer

A point mutation involves the substitution, insertion, or deletion of a single nucleotide in the DNA sequence.

Gaokao Exam Practice Test

Gaokao Exam Practice Test

Gaokao Exam Biology: Genetics and Evolution